The Sci Fi channel’s most popular series opens a new chapter with the two-hour season premiere of “Stargate SG-1” (8 p.m., Sci Fi). You needn’t have followed the series, or have seen the 1994 movie version of “Stargate,” to keep up with the action.

For the uninitiated, a stargate is an ancient portal that allows a scientific military team to travel through the universe via cosmic wormholes. Early Egyptians were hip to this technology, hence the device’s groovy hieroglyphics. Next Friday, July 16, the team walks through the portal to find the legendary city of Atlantis in some far-off galaxy and launch the spin-off series “Stargate Atlantis.”

The farfetched premise of “Stargate” is thoroughly grounded in the show’s impressive production values and consistent attention to the technical details (however contrived and concocted) of wormhole travel.

As fans of “SG-1” recall, Col. Jack O’Neill’s (Richard Dean Anderson) fate was very much in doubt at the conclusion of season seven. Does he return in one piece from his frozen state of bio-stasis? I’ll never tell.

Tonight’s other highlights

• U.S. Olympic swimming trials (7 p.m., NBC).
• On a repeat “Dateline” (8 p.m., NBC): An interview with Osama bin Laden’s brother, Yeslam.
• Scheduled on “48 Hours Investigates” (9 p.m., CBS): older women dating younger men, other sex trends.

Late night

Bill Murray and P.J. Harvey appear on a repeat “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno greets Tommy Chong, Brandi Chastain and Mia Hamm on “The Tonight Show” (10:35 p.m., NBC).